Driver's side heat has cool

[rlumsd]

Spent some time using search but didnt find this... '92 300E with single temp climate control, With Engine temp @80 C, drivers floor vent has cool air mixed in when on heat. Passenger's side and both upper side vents feel good and warm. Enabling the recirc feature seems to help some. Recent very cold days make this issue much more noticeable. What should I do first to stop the cool air on the drivers side??

[dpetryk]

Some of the vacuum operated actuators are not working properly. Could be the operators or the vaccuum valves.

[rlumsd]

Hopefully I wont sound to uninformed but where and what are those ? Are these above average owner replaceable parts?

[dpetryk]

They are located in and around the big black box containing the heater and air conditioning radiators which is right behind the center console. They direct the air to the appropriate vent depending on the mode. All the hose ducts eminate from there. Some are very difficult to get access to, others are not. They can be checked with a vacuum pump/tester relatively easily. But good documentation and understanding of the climate control system is a must.